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Published: 2010-12-17 00:00:00

An Environment Waikato spraying programme targeting yellow flag iris along the Waikato River around Huntly and downstream is due to get underway in February next year.

Yellow flag iris is an exotic, leafy ground cover plant, with flax-like leaves, that can grow up to two metres high under ideal conditions.

It is toxic to livestock, chokes out and prevents establishment of native plant species, reduces the food supply available for native animals and leads to nutrients getting into the river when yellow flag iris foliage dies off annually.

Yellow flag iris is a “total control” plant under EW’s regional pest management strategy meaning that land owners are responsible for removing it when it is found.

EW has detected yellow flag iris on around 500 hectares of land in Huntly and further downstream.  In some parts there is a blanket of the pest plant covering river margin and pasture.

In February, EW will begin yellow flag iris eradication work on more than 200 hectares of land it manages in Huntly and downstream. The land contains flood control assets such as stopbanks and spillways. All the work to be done is on land and river margin adjacent to the lower Waikato River main channel. After treatment, follow up planting of natives is planned by Waikato RiverCare.

The first area of land to be sprayed starting in February involves a stretch of around two and a half kilometres of riverside. At the same time as yellow flag iris is tackled, EW will also take the opportunity to remove undesirable exotic plants such as alder, willow and a range of other weeds. It is hoped the rest of the more than 200 hectares of EW-managed land will be progressively treated after that over a period of years, depending on funding and work priorities.

The remaining approximately 300 hectares of land in the area with yellow flag iris is also around and downstream of Huntly and is privately owned. EW has written to the land owners involved reminding them that yellow flag iris must be controlled.

“EW is getting on with tackling yellow flag iris on the land it is managing,” said river and catchment services group manager Scott Fowlds.

“We will now seek to work with the private land owners on addressing the yellow flag iris on their properties.

“It’s important that we all get on top of this pest plant if we want to ensure that Waikato River margins in the area aren’t further damaged by the spread of yellow flag iris.”

For further public information on the yellow flag iris spraying programme contact Louisa Alix on 0800 800 401 or email